When a vehicle attempts to follow a planned route and schedule, it is often appropriate to monitor adherence by the vehicle to the route and/or schedule, especially if the vehicle is a common carrier, such as a public transit bus or railway train. In such instance, the vehicle schedule is often published, and some of the public relies on the schedule in planning for its transportation needs. If the route or schedule is regularly disrupted or modified substantially, monitoring route and schedule adherence will identify the problem and perhaps provide a solution, through modification of the published schedule and/or route.
Monitoring adherence to a route or schedule is not straightforward if the vehicle can make, or not make, many stops or slight excursions in response to the needs of its users. Some systems have been proposed for monitoring the present and past locations of a vehicle. In U.S. Pat. No. 4,651,157, Gray et al disclose a security monitoring and tracking system for a terrestrial or marine vehicle that uses navigational information provided an array of by a Loran-C or satellite-based signal transmitters. These signals are received by a transceiver mounted on the vehicle and are retransmitted to a central station for analysis and post-processing of the signals, to determine the latitude and longitude of the vehicle at the time the signals were originally received thereat.
Olsen et al, in U.S. Pat. No. 4,814,711, discloses a survey system for collection of real time data from a plurality of survey vehicles, each of which determines its present location using global positioning system (GPS) signals received from a plurality of GPS satellites. A central station periodically polls each survey vehicle and receives that survey vehicle's present location coordinates by radio wave communication. The central station compares that vehicle's path with a survey pattern assigned to that vehicle. The geophysical or survey data measured by a vehicle are also received by the central station and are coordinated with that vehicle's location at the time were taken.
A vehicle tracking system, using an on-board Loran or GPS navigational system, is disclosed in U.S. Pat. No. 5,014,206, issued to Scribner et al. The vehicle receives Loran or GPS signals and determines its present location coordinates but transmits these coordinates to a central station only upon the occurrence of a specified event or events. This event might be stopping of the vehicle for a time interval of length more than a selected threshold or opening of the cargo doors or any other unusual event.
Harker et al disclose a method for analyzing transportation schedules of a transportation vehicle, such as a railway train or bus, to produce optimized schedules, in U.S. Pat. No. 5,177,684. The method uses information on the vehicle's assigned path and average speed and mobility of the vehicle and determines a realistic, optimum schedule, including arrival and departure times, that the vehicle can adhere to along that path.
U.S. Pat. No. 5,191,341, issued to Gouard et al, discloses a tracking system for a plurality of marine vessels, using two or more radio beacons and a fixed or mobile central station. Each marine receives signals from each beacon and relays these signals to the central station for determination of the present location of the vessel, using standard intersections of two or more hyperbolas for this purpose. A vessel's present location is tracked for routing, entrance into and exit from a harbor, arrival at and departure from a pier, and other similar purposes.
Navigation apparatus that stores location coordinates for a sequence of intermediate or final destination points on a non-volatile memory, such as a CD-ROM, is disclosed by Nimura et al in U.S. Pat. No. 5,231,584. A vehicle or traveller activates the apparatus at a departure point, then communicates its arrival at one or more designated intermediate or final destination points by pressing a button at the time of arrival. The apparatus does not track time of arrival and provides little direct information on the present location of the vehicle or traveller between a departure point and the next destination point.
Stanifer et al, in U.S. Pat. No. 5,243,530, disclose a system for tracking a plurality of terrestrial, marine or airborne vehicles, using a local area network and packet communication of location information. Loran-C signals are received by a receiver/processor/transmitter on a vehicle, the vehicle's present location is determined, and this location information is transmitted to a central station, using LAN packet protocols, acknowledgment signals and backoff/retransmission procedures that are standard in the LAN art. If a given vehicle's present location is not received by the central station within a time interval of selected length, the central station requests transmission of the present location from that vehicle.
A navigation system that provides off-route detection and route re-optimization is disclosed in U.S. Pat. No. 5,262,775, issued to Tamai et al. The system is mounted on a vehicle and uses GPS or Loran signals to determine the present location of the vehicle. When the vehicle is determined to be off-course, relative to its planned route, by more than a selected threshold distance, the system notifies the vehicle operator of this deviation and computes and displays a new optimized route, beginning at the vehicle's present location.
In U.S. Pat. No. 5,272,638, Martin et al disclose a system for optimizing a travel route for a vehicle, based on a shortest-path algorithm of Dijkstra (which is neither explained nor referenced in the patent). The system uses a roadway database, with distances between roadway decision points included, and determines the order of destination points and the shortest route to be followed by a vehicle, such as a truck making deliveries to a plurality of destinations. The present location of the vehicle is not tracked between intermediate destination points along the route.
A navigation system using audio communication between the system and an operator of a vehicle is disclosed in U.S. Pat. No. 5,274,560, issued to LaRue. The system is provided with a roadway database, a departure point and a destination point. The system uses artificial intelligence techniques to determine the optimum route to be followed, then communicates with the vehicle operator to direct the vehicle along the chosen route, unless overridden by voice command from the vehicle operator. The present location of the vehicle is not tracked by an independent ground-based or satellite-based location determination system along the route.
What is needed is an approach that allows more focused monitoring of the vehicle's present location, based on the present time and the route and schedule nominally followed by the vehicle. Preferably, the frequency of reporting of the location and time of observation should be relatively low when the vehicle stays within its allocated ranges in space and time, and this frequency should become appreciable only where the vehicle manifests frequent or continuing above-threshold excursions relative to its planned route and/or schedule. Preferably, the approach should allow use of other location aids, such as a vehicle odometer, or use of other methods, such as dead reckoning, to supplement and improve the accuracy of the location and/or observation time determined by the monitoring system.